| 摘要 |
A bar code comprises a data track (3; 104; 205; 304) and a clock track (4; 103; 204; 303). The separate clock track (4; 103; 204; 303) means that the sampling of the be synchronised with the movement of the bar code. The addition of a reference track (5; 105; 206) enables the forming of the bar code into a ring containing a plurality of repetitions of the encoded data. The bar codes may form a continuous ring themselves or be discrete blocks arranged in a ring. Consequently, a coin-like object (1; 101; 201), such as a coin or a token, can be marked with the bar code and the bar code can be read as the coin-like object (1; 101; 201) falls past an optical sensing station (26, 27, 226, 227) with sensors for reading respectively the clock data and reference tracks.
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